This invention relates to chemical mechanical planarization (CMP, chemical mechanical polishing) for use in semiconductor manufacture. In particular, the invention relates to use of CMP in low (e.g., 22 nm) technology node applications.
CMP processing employing a barrier CMP slurry at stage 2 is often used to remove and planarize excess metal layers and other films on the surface of the patterned wafers to achieve global planarization.
When such CMP processing is utilized, a multi-step CMP process may be employed involving the initial removal and planarization of the copper overburden, referred to as a step 1 copper CMP process, followed by a barrier layer CMP process. The barrier layer CMP process is frequently referred to as a barrier or step 2 CMP process.
A specific featured distortion that is unsuitable for semiconductor manufacturing is the damage to copper vias or metal lines caused by the further corrosion of chemical components interacting with copper vias or metal lines in a chemical mechanical polishing process. Therefore, it is very important to identify and use suitable corrosion inhibitor(s) in a CMP slurry to reduce and control further corrosion of copper vias or trenches during and subsequent to chemical mechanical polishing processes.
In step 2 CMP processes, a barrier CMP slurry is used for the polishing process. The chemical reactions involved in using a barrier CMP slurry include: oxidation reactions induced by the oxidant used in the barrier CMP slurry, for example, H2O2. The surfaces of copper vias or trenches, and barrier material, such as Ta, are oxidized into the relative metal oxide films, typically, metal copper is oxidized into a mixture of cuprous and cupric oxides, and Ta is oxidized to Ta2O5 (the preferred oxide form for Ta). In most cases, chelators or ligands which can be chemically bonded to the copper cations and tantalum cations are used in barrier CMP slurry to accelerate the dissolution of copper oxide and tantalum oxide to yield the desirable removal rates of copper vias, trenches and barrier layer. Typically, abrasives are also used in most barrier CMP slurries; the abrasives with variable particle size provide mechanical friction forces between polishing pad and wafer surface under applied pressure.
In general, freshly polished copper vias or trenches will continue interacting with chemical components used in the CMP slurry to undergo further corrosion process. The further corroded copper vias or trenches will cause some defect issues for the subsequent integration of IC chips. Therefore, a corrosion inhibitor is used in the barrier CMP slurry to protect the copper vias or trenches during and after chemical mechanical polishing process from further corrosion. For example, BTA (1-H-1,2,3-benzotriazole) is widely known and used as a corrosion inhibitor in CMP slurries.
Ideally, a monolayer protection formed by the corrosion inhibitor used in a CMP slurry (e.g., barrier slurry) is preferred, but in fact, sometimes, BTA tends to form multilayer protective films on the surface of copper vias or trenches through coordination reactions. BTA also becomes less effective in corrosion inhibition when used in basic solutions. The commonly recognized passivation mechanism for BTA on the surface of polished copper vias or trenches involved the formation of a thin layer of polymeric BTA-Cun+ complexes or tetramer of BTA-Cun+ complexes.
Another drawback of BTA as a corrosion inhibitor is that the removal rates of copper vias or trenches generally will be undesirably reduced when the concentration of BTA is increased due to the formation of insoluble film of polymeric BTA-Cun+ complexes. Therefore, there is a significant need for finding new corrosion inhibitors that protect metal surfaces from corroding both during and after CMP processing but which do not have the above mentioned drawbacks that BTA and related corrosion inhibitors have. The present invention addresses this need by providing effective new corrosion inhibitors that do not have the drawbacks associated with BTA.